Systems and methods for protecting power conversion systems from thermal runaway

ABSTRACT

System and method for protecting a power conversion system. An example system controller includes a protection component and a driving component. The protection component is configured to receive a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, process information associated with the feedback signal, the reference signal, and the demagnetization signal, and generate a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal. The demagnetization signal is related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The driving component is configured to receive the protection signal and output a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/151,209, filed Jan. 9, 2014, which claims priority to Chinese PatentApplication No. 201310656906.4, filed Dec.6, 2013, both of theabove-referenced applications being commonly assigned and incorporatedby reference herein for all purposes.

This application is related to U.S. patent application Ser. Nos.13/857,836, 13/071,384, 12/581,775, and 12/502,866, incorporated byreference herein for all purposes.

2. BACKGROUND OF THE INVENTION

Certain embodiments of the present invention are directed to integratedcircuits. More particularly, some embodiments of the invention provide asystem and method for protecting one or more circuit components. Merelyby way of example, some embodiments of the invention have been appliedto power conversion systems. But it would be recognized that theinvention has a much broader range of applicability.

Schottky rectifying diodes with low forward voltages are often used inpower conversion systems to improve system efficiency. Generally, aconventional power conversion system often uses a transformer to isolatethe input voltage on the primary side and the output voltage on thesecondary side. To regulate the output voltage, certain components, suchas TL431 and an opto-coupler, can be used to transmit a feedback signalfrom the secondary side to a controller chip on the primary side.Alternatively, the output voltage on the secondary side can be imaged tothe primary side, so the output voltage is controlled by directlyadjusting some parameters on the primary side. Then, some components,such as TL431 and an opto-coupler, can be omitted to reduce the systemcosts.

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system with primary-side sensing and regulation. The powerconversion system 100 includes a primary winding 110, a secondarywinding 112, an auxiliary winding 114, a power switch 120, a currentsensing resistor 130, an equivalent resistor 140 for an output cable,resistors 150 and 152, and a Schottky rectifying diode 160. For example,the power switch 120 is a bipolar junction transistor. In anotherexample, the power switch 120 is a MOS transistor.

To regulate the output voltage within a predetermined range, informationrelated to the output voltage and the output loading often needs to beextracted. For example, when the power conversion system 100 operates ina discontinuous conduction mode (DCM), such information can be extractedthrough the auxiliary winding 114. When the power switch 120 is turnedon, the energy is stored in the secondary winding 112. Then, when thepower switch 120 is turned off, the stored energy is released to theoutput terminal during a demagnetization process. The voltage of theauxiliary winding 114 maps the output voltage on the secondary side asshown below.

$\begin{matrix}{V_{FB} = {{\frac{R_{2}}{R_{1} + R_{2}} \times V_{aux}} = {k \times n \times \left( {V_{0} + V_{F} + {I_{0} \times R_{eq}}} \right)}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$where V_(FB) represents a voltage at a node 154, and V_(aux) representsthe voltage of the auxiliary winding 114. R₁ and R₂ represent theresistance values of the resistors 150 and 152 respectively.Additionally, n represents a turns ratio between the auxiliary winding114 and the secondary winding 112. Specifically, n is equal to thenumber of turns of the auxiliary winding 114 divided by the number ofturns of the secondary winding 112. V_(o) and I_(o) represent the outputvoltage and the output current respectively. Moreover, V_(F) representsthe forward voltage of the rectifying diode 160, and R_(eq) representsthe resistance value of the equivalent resistor 140. Also, k representsa feedback coefficient as shown below:

$\begin{matrix}{k = \frac{R_{2}}{R_{1} + R_{2}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

FIG. 2 is a simplified diagram showing a conventional operationmechanism for the flyback power conversion system 100. As shown in FIG.2, the controller chip of the conversion system 100 uses asample-and-hold mechanism. When the demagnetization process on thesecondary side is almost completed and the current I_(sec) of thesecondary winding 112 almost becomes zero, the voltage V_(aux) of theauxiliary winding 114 is sampled at, for example, point A of FIG. 2. Thesampled voltage value is usually held until the next voltage sampling isperformed. Through a negative feedback loop, the sampled voltage valuecan become equal to a reference voltage V_(ref). Therefore,V _(FB) =V _(ref)  (Equation 3)

Combining Equations 1 and 3, the following can be obtained:

$\begin{matrix}{V_{0} = {\frac{V_{ref}}{k \times n} - V_{F} - {I_{0} \times R_{eq}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$Based on Equation 4, the output voltage decreases with the increasingoutput current.

But thermal runaway may occur in the Schottky diode 160 if thetemperature of the diode 160 exceeds a threshold, and a reverse leakagecurrent increases in magnitude drastically. If the output load of thepower conversion system 100 is reduced, the reverse leakage currentcontinues to increase in magnitude and the temperature of the diode 160does not decrease. As such, once the thermal runaway occurs in theSchottky diode 160, the temperature of the diode 160 keeps higher than anormal operating temperature even if the output load is reduced, whichmay cause safety problems. For example, the outer shell of the powerconversion system 100 may be melted due to the high temperature of theSchottky diode 160.

Hence it is highly desirable to improve the techniques of systemprotection.

3. BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the present invention are directed to integratedcircuits. More particularly, some embodiments of the invention provide asystem and method for protecting one or more circuit components. Merelyby way of example, some embodiments of the invention have been appliedto power conversion systems. But it would be recognized that theinvention has a much broader range of applicability.

According to one embodiment, a system controller for protecting a powerconversion system includes a protection component and a drivingcomponent. The protection component is configured to receive a feedbacksignal, a reference signal, and a demagnetization signal generated basedon at least information associated with the feedback signal, processinformation associated with the feedback signal, the reference signal,and the demagnetization signal, and generate a protection signal basedon at least information associated with the feedback signal, thereference signal, and the demagnetization signal. The demagnetizationsignal is related to multiple demagnetization periods of the powerconversion system, the multiple demagnetization periods including afirst demagnetization period and a second demagnetization period. Thedriving component is configured to receive the protection signal andoutput a drive signal to a switch configured to affect a current flowingthrough a primary winding of the power conversion system. The protectioncomponent is further configured to: process information associated withthe feedback signal and the reference signal during a first detectionperiod, the first detection period including a first starting time and afirst ending time, the first starting time being at or after a firstdemagnetization end of the first demagnetization period, determine,during the first detection period, a first number of times that thefeedback signal changes from being smaller than the reference signal tobeing larger than the reference signal in magnitude, and determinewhether the first number of times exceeds a predetermined threshold atthe first ending time. The protection component and the drivingcomponent are further configured to, in response to the first number oftimes not exceeding the predetermined threshold at the first endingtime, output the drive signal to cause the switch to open and remainopen in order to protect the power conversion system.

According to another embodiment, a system controller for protecting apower conversion system includes a protection component and a drivingcomponent. The protection component is configured to receive a feedbacksignal, a reference signal, and a demagnetization signal generated basedon at least information associated with the feedback signal, processinformation associated with the feedback signal, the reference signal,and the demagnetization signal, and generate a protection signal basedon at least information associated with the feedback signal, thereference signal, and the demagnetization signal. The demagnetizationsignal is related to multiple demagnetization periods of the powerconversion system, the multiple demagnetization periods including afirst demagnetization period and a second demagnetization period. Thedriving component is configured to receive the protection signal andoutput a drive signal to a switch configured to affect a current flowingthrough a primary winding of the power conversion system. The protectioncomponent is further configured to: process information associated withthe feedback signal and the reference signal during a first detectionperiod, the first detection period including a first starting time and afirst ending time, the first starting time being at or after a firstdemagnetization end of the first demagnetization period, determine,during the first detection period, a first number of times that thefeedback signal changes from being larger than the reference signal tobeing smaller than the reference signal in magnitude, and determinewhether the first number of times exceeds a predetermined threshold atthe first ending time. The protection component and the drivingcomponent are further configured to, in response to the first number oftimes not exceeding the predetermined threshold at the first endingtime, output the drive signal to cause the switch to open and remainopen in order to protect the power conversion system.

According to yet another embodiment, a method for protecting a powerconversion system includes: receiving a feedback signal, a referencesignal, and a demagnetization signal generated based on at leastinformation associated with the feedback signal, processing informationassociated with the feedback signal, the reference signal, and thedemagnetization signal, and generating a protection signal based on atleast information associated with the feedback signal, the referencesignal, and the demagnetization signal, the demagnetization signal beingrelated to multiple demagnetization periods of the power conversionsystem, the multiple demagnetization periods including a firstdemagnetization period and a second demagnetization period. The methodadditionally includes: receiving the protection signal, processinginformation associated with the protection signal, and outputting adrive signal to a switch configured to affect a current flowing througha primary winding of the power conversion system. The processinginformation associated with the feedback signal, the reference signal,and the demagnetization signal includes: processing informationassociated with the feedback signal and the reference signal during afirst detection period, the first detection period including a firststarting time and a first ending time, the first starting time being ator after a first demagnetization end of the first demagnetizationperiod, determining, during the first detection period, a first numberof times that the feedback signal changes from being smaller than thereference signal to being larger than the reference signal in magnitude,and determining whether the first number of times exceeds apredetermined threshold at the first ending time. The outputting a drivesignal to a switch configured to affect a current flowing through aprimary winding of the power conversion system includes: in response tothe first number of times not exceeding the predetermined threshold atthe first ending time, outputting the drive signal to cause the switchto open and remain open in order to protect the power conversion system.

According to yet another embodiment, a method for protecting a powerconversion system includes: receiving a feedback signal, a referencesignal, and a demagnetization signal generated based on at leastinformation associated with the feedback signal, processing informationassociated with the feedback signal, the reference signal, and thedemagnetization signal, and generating a protection signal based on atleast information associated with the feedback signal, the referencesignal, and the demagnetization signal, the demagnetization signal beingrelated to multiple demagnetization periods of the power conversionsystem, the multiple demagnetization periods including a firstdemagnetization period and a second demagnetization period. The methodfurther includes: receiving the protection signal, processinginformation associated with the protection signal, and outputting adrive signal to a switch configured to affect a current flowing througha primary winding of the power conversion system. The processinginformation associated with the feedback signal, the reference signal,and the demagnetization signal includes: processing informationassociated with the feedback signal and the reference signal during afirst detection period, the first detection period including a firststarting time and a first ending time, the first starting time being ator after a first demagnetization end of the first demagnetizationperiod, determining, during the first detection period, a first numberof times that the feedback signal changes from being larger than thereference signal to being larger than the reference signal in magnitude,and determining whether the first number of times exceeds apredetermined threshold at the first ending time. The outputting a drivesignal to a switch configured to affect a current flowing through aprimary winding of the power conversion system includes: in response tothe first number of times not exceeding the predetermined threshold atthe first ending time, outputting the drive signal to cause the switchto open and remain open in order to protect the power conversion system.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system with primary-side sensing and regulation.

FIG. 2 is a simplified diagram showing a conventional operationmechanism for the flyback power conversion system as shown in FIG. 1.

FIG. 3 is a simplified diagram showing a power conversion system withprimary-side sensing and regulation.

FIG. 4 is a simplified diagram showing at least certain components of aconstant-current component as part of the power conversion system asshown in FIG. 3.

FIG. 5 is a simplified timing diagram for the power conversion system asshown in FIG. 3 in a constant-current mode.

FIG. 6 is a simplified timing diagram for the power conversion system asshown in FIG. 3 in a constant-voltage mode.

FIG. 7 is a simplified timing diagram for the power conversion system asshown in FIG. 3 in a constant-voltage mode under thermal runaway of arectifying diode according to one embodiment.

FIG. 8 is a simplified diagram showing a power conversion system withprimary-side sensing and regulation according to an embodiment of thepresent invention.

FIG. 9 is a simplified diagram showing a protection component as part ofthe power conversion system as shown in FIG. 8 according to anembodiment of the present invention.

FIG. 10 is a simplified timing diagram for the power conversion systemas shown in FIG. 8 according to an embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention are directed to integratedcircuits. More particularly, some embodiments of the invention provide asystem and method for protecting one or more circuit components. Merelyby way of example, some embodiments of the invention have been appliedto power conversion systems. But it would be recognized that theinvention has a much broader range of applicability.

FIG. 3 is a simplified diagram showing a power conversion system withprimary-side sensing and regulation. The power conversion system 300includes a primary winding 310, a secondary winding 312, an auxiliarywinding 314, a power switch 320, a current sensing resistor 330, anequivalent resistor 340 for an output cable, resistors 350 and 352, arectifying diode 360, and a controller 370. The controller 370 includesa sampling component 302, a demagnetization detector 304, a capacitor306, a switch 307, a reference-signal generator 308, aramp-generator-and-oscillator component 316, an AND gate 318, a drivingcomponent 322, an OR gate 324, comparators 326 and 328, a flip-flopcomponent 336, a leading edge blanking (LEB) component 386, resistors384 and 388, an error amplifier 390, a modulation component 392, and aconstant-current (CC) component 394. For example, the power switch 320is a bipolar transistor. In another example, the power switch 320 is aMOS transistor. In yet another example, the controller 370 includesterminals 372, 374, 376, 378 and 380. In yet another example, therectifying diode 360 is a Schottky diode. For example, theramp-generator-and-oscillator component 316 generates a clock signal 369and a ramp signal 368.

For example, the auxiliary winding 314 is magnetically coupled to thesecondary winding 312, which, with one or more other components,generates an output voltage 393. In another example, information relatedto the output voltage is processed by a voltage divider of the resistors350 and 352, and is used to generate a feedback voltage 354, which isreceived by the terminal 372 (e.g., terminal FB) of the controller 370.In another example, the sampling component 302 samples the feedbackvoltage 354 and the sampled signal is held at the capacitor 306. As anexample, the error amplifier 390 compares the sampled-and-held voltage362 with a reference signal 364 generated by the reference-signalgenerator 308, and outputs a comparison signal 366 associated with theerror of the sampled-and-held voltage 362 with respect to the referencesignal 364. As another example, the comparison signal 366 is received bythe modulation component 392. In some embodiments, the modulationcomponent 392 receives the ramp signal 368 and/or the clock signal 369from the ramp-generator-and-oscillator component 316 and outputs asignal 356 (e.g., CV_ctrl).

For example, the comparison signal 366 is used to control the pulsewidth for pulse-width modulation (PWM) and/or the switching frequencyfor pulse-frequency modulation (PFM) in order to regulate the outputvoltage in a constant-voltage mode. In another example, thedemagnetization detector 304 determines the duration of ademagnetization period based on the feedback voltage 354 and outputs adetection signal 358 to the constant-current component 394 whichgenerates a signal 346 (e.g., CC_ctrl). In yet another example, both thesignal 356 and the signal 346 are received by the AND gate 318 to affectthe flip-flop component 336 and in turn the driving component 322. Inyet another example, the driving component 322 outputs a drive signal348 through the terminal 376 to affect the status of the switch 320. Inyet another example, a primary current 396 flowing through the primarywinding 310 is sensed using the resistor 330, and a current-sensingsignal 342 is generated through the LEB component 386 and received bythe comparators 326 and 328. In yet another example, the comparator 326receives a threshold voltage 332 (e.g., V_(thocp)), and the comparator328 receives another threshold voltage 301 associated with thecomparison signal 366 (e.g., V_(comp)). In yet another example, thecomparator 326 and the comparator 328 output comparison signals 334 and338 respectively, to the OR gate 324 to affect the flip-flop component336. As an example, when the sampled-and-held voltage 362 is smallerthan the reference signal 364 in magnitude, the error amplifier 390outputs the comparison signal 366 at a logic high level. The powerconversion system 300 operates in a constant-current mode, in someembodiments. For example, when the sampled-and-held voltage 362 is equalto the reference signal 364 in magnitude, the comparison signal 366 hasa fixed magnitude. The power conversion system 300 operates in theconstant-voltage mode, in certain embodiments.

FIG. 4 is a simplified diagram showing at least certain components ofthe constant-current component 394 as part of the power conversionsystem 300. The constant-current component 394 includes a NOT gate 402,current sources 404 and 406, a switch 408, a capacitor 414, a comparator410 and a reference-signal generator 412.

For example, when the detection signal 358 is at a logic low level, theswitch 408 is open (e.g., being turned off) and the switch 416 is closed(e.g., being turned on). In another example, the current source 404provides a current 418 (e.g., I₀) to charge the capacitor 414, and inresponse a signal 420 increases in magnitude. As an example, when thedetection signal 358 is at a logic high level, the switch 416 is open(e.g., being turned off) and the switch 408 is closed (e.g., beingturned on). As another example, the capacitor 414 is discharged throughthe current source 406 which provides a current 424 (e.g., I₁), and thesignal 420 decreases in magnitude. For example, the comparator 410receives the signal 420 and a reference signal 422 generated by thereference-signal generator 412 and outputs the signal 346. In certainembodiments, the modulation component 392 receives the clock signal 369and/or the ramp signal 368 from the ramp-generator-and-oscillatorcomponent 316.

FIG. 5 is a simplified timing diagram for the power conversion system300 in a constant-current mode. The waveform 602 represents the feedbackvoltage 354 as a function of time, the waveform 604 represents thedetection signal 358 as a function of time, and the waveform 606represents the signal 420 as a function of time. The waveform 608represents the signal 346 (e.g., CC_ctrl) as a function of time, thewaveform 610 represents the signal 348 as a function of time, thewaveform 612 represents the current-sensing signal 342 as a function oftime, and the waveform 618 represents the signal 356 (e.g., CV_ctrl) asa function of time.

Four time periods are shown in FIG. 5. A switching period T_(s1)includes an on-time period T_(on1) and an off-time period T_(off1) andcorresponds to a modulation frequency. The off-time period T_(off1)includes a demagnetization period T_(demag1). The on-time period T_(on1)starts at time t₀ and ends at time t₁, the demagnetization periodT_(demag1) starts at the time t₁ and ends at time t₂, and the off-timeperiod T_(off1) starts at the time t₁ and ends at time t₃. For example,t₀≦t₁≦t₂≦t₃.

For example, as shown in the waveform 618, the signal 356 (e.g.,CC_ctrl) keeps at a magnitude (e.g., 1) without changing in theconstant-current mode. In another example, at the beginning of theon-time period T_(on1) (e.g., at t₀), the signal 348 changes from alogic low level to a logic high level (e.g., as shown by the waveform610), and in response the switch 320 is closed (e.g., being turned on).In yet another example, the transformer including the primary winding310 and the secondary winding 312 stores energy, and the primary current396 increases in magnitude (e.g., linearly). In yet another example, thecurrent-sensing signal 342 increases in magnitude (e.g., as shown by thewaveform 612).

As an example, the threshold voltage 332 (e.g., V_(thocp)) is smaller inmagnitude than the threshold 301 (e.g., V_(div)). In another example,when the current-sensing signal 342 reaches the threshold voltage 332(e.g., V_(thocp)), the comparator 326 changes the comparison signal 334in order to turn off the switch 320. As another example, during theon-time period, the detection signal 358 (e.g., Demag) keeps at a logiclow level (e.g., as shown by the waveform 604). As yet another example,the switch 408 is open (e.g., being turned off) and the switch 416 isclosed (e.g., being turned on). As yet another example, the capacitor414 is charged (e.g., at I₀), and the signal 420 increases in magnitude(e.g., linearly) as shown by the waveform 606.

In one example, at the beginning of the demagnetization periodT_(demag1) (e.g., at t₁), the signal 348 changes from the logic highlevel to the logic low level (e.g., as shown by the waveform 610), andin response the switch 320 is opened (e.g., being turned off). Inanother example, the energy stored in the transformer is released to theoutput terminal, and the demagnetization process begins. In yet anotherexample, a secondary current 397 that flows through the secondarywinding 312 decreases in magnitude (e.g., linearly). In yet anotherexample, a voltage 395 at the auxiliary winding 314 maps the outputvoltage 393, and the feedback voltage 354 is generated through thevoltage divider including the resistors 350 and 352. As an example, whenthe secondary current decreases to a low magnitude (e.g., 0), thedemagnetization process ends. As another example, the transformerincluding the primary winding 310 and the secondary winding 312 enters aresonant status. As yet another example, a voltage 395 at the auxiliarywinding 314 has an approximate sinusoidal waveform. In an example,during the demagnetization period, the detection signal 358 (e.g.,Demag) keeps at a logic high level (e.g., as shown by the waveform 604).In yet another example, the switch 416 is opened (e.g., being turnedoff) and the switch 408 is closed (e.g., being turned on). In yetanother example, the capacitor 414 is discharged (e.g., at I₁), and thesignal 420 decreases in magnitude (e.g., linearly) as shown by thewaveform 606. In yet another example, if the feedback voltage 354becomes larger than the reference signal 516 (e.g., 0.1 V) in magnitude,it is determined that the demagnetization process has begun. In yetanother example, if the feedback voltage 354 becomes smaller than thereference signal 516 (e.g., 0.1 V) in magnitude, it is determined thatthe demagnetization process has ended.

As one example, after the demagnetization process ends (e.g., at t₂),the detection signal 358 changes from the logic high level to the logiclow level (e.g., as shown by the waveform 604). As another example, theswitch 408 is open (e.g., being turned off) and the switch 416 is closed(e.g., being turned on). As yet another example, the capacitor 414 ischarged again, and the signal 420 increases in magnitude (e.g.,linearly) again as shown by the waveform 606. As yet another example,when the signal 420 becomes larger than a threshold voltage 614 (e.g.,the reference signal 422) in magnitude (e.g., at t₃), the comparator 410changes the signal 346 (e.g., CC_ctrl) from the logic low level to thelogic high level (e.g., as shown by the waveform 608). As yet anotherexample, in response to the signal 346 being at the logic high level,the driving component 322 changes the signal 348 from the logic lowlevel to the logic high level (e.g., at t₃ as shown by the waveform610).

FIG. 6 is a simplified timing diagram for the power conversion system300 in a constant-voltage mode. The waveform 702 represents the feedbackvoltage 354 as a function of time, the waveform 704 represents thedetection signal 358 as a function of time, and the waveform 706represents the signal 420 as a function of time. The waveform 708represents the signal 346 (e.g., CC_ctrl) as a function of time, thewaveform 716 represents the signal 368 as a function of time, and thewaveform 720 represents the comparison signal 366 as a function of time.In addition, the waveform 718 represents the signal 356 (e.g., CV_ctrl)as a function of time, the waveform 710 represents the signal 348 as afunction of time, and the waveform 712 represents the current-sensingsignal 342 as a function of time.

Four time periods are shown in FIG. 6. A switching period T_(s2)includes an on-time period T_(on2) and an off-time period T_(off2) andcorresponds to a modulation frequency. The off-time period T_(off2)includes a demagnetization period T_(demag2). The on-time period T_(on2)starts at time t₆ and ends at time t₇, the demagnetization periodT_(demag2) starts at the time t₇ and ends at time t₈, and the off-timeperiod T_(off2) starts at the time t₇ and ends at time t₁₀. For example,t₆≦t₇≦t₈≦t₉≦t₁₀.

For example, at the beginning of the on-time period T_(on2) (e.g., att₆), the signal 348 changes from a logic low level to a logic high level(e.g., as shown by the waveform 710), and in response the switch 320 isclosed (e.g., being turned on). In yet another example, the transformerincluding the primary winding 310 and the secondary winding 312 storesenergy, and the primary current 396 increases in magnitude (e.g.,linearly). In yet another example, the current-sensing signal 342increases in magnitude (e.g., as shown by the waveform 712). In yetanother example, at the beginning of the on-time period T_(on2) (e.g.,at t₆), the signal 356 changes from the logic low level to the logichigh level (e.g., as shown by the waveform 718) in order to close theswitch 320.

As an example, the threshold voltage 332 (e.g., V_(thocp)) is larger inmagnitude than the threshold 301 (e.g., V_(div)). In another example,when the current-sensing signal 342 reaches the threshold voltage 301(e.g., V_(div)), the comparator 328 changes the comparison signal 338 inorder to turn off the switch 320. As another example, during the on-timeperiod, the detection signal 358 (e.g., Demag) keeps at a logic lowlevel (e.g., as shown by the waveform 704). As yet another example, theswitch 408 is open (e.g., being turned off) and the switch 416 is closed(e.g., being turned on). As yet another example, the capacitor 414 ischarged (e.g., at I₀), and the signal 420 increases in magnitude (e.g.,linearly) as shown by the waveform 706.

In one example, at the beginning of the demagnetization periodT_(demag2) (e.g., at t₇), the signal 348 changes from the logic highlevel to the logic low level (e.g., as shown by the waveform 710), andin response the switch 320 is opened (e.g., being turned off). Inanother example, the energy stored in the transformer is released to theoutput terminal, and the demagnetization process begins. In yet anotherexample, a secondary current 397 that flows through the secondarywinding 312 decreases in magnitude (e.g., linearly). In yet anotherexample, a voltage 395 at the auxiliary winding 314 maps the outputvoltage 393, and the feedback voltage 354 is generated through thevoltage divider including the resistors 350 and 352. As an example, whenthe secondary current decreases to the low magnitude (e.g., 0), thedemagnetization process ends. As another example, the transformerincluding the primary winding 310 and the secondary winding 312 entersthe resonant status. As yet another example, the voltage 395 at theauxiliary winding 314 has an approximate sinusoidal waveform. In anexample, during the demagnetization period, the detection signal 358(e.g., Demag) keeps at the logic high level (e.g., as shown by thewaveform 704). In yet another example, the switch 416 is opened (e.g.,being turned off) and the switch 408 is closed (e.g., being turned on).In yet another example, the capacitor 414 is discharged (e.g., at I₁),and the signal 420 decreases in magnitude (e.g., linearly) as shown bythe waveform 706. In yet another example, if the feedback voltage 354becomes larger than the reference signal 516 (e.g., 0.1 V) in magnitude,it is determined that the demagnetization process has begun. In yetanother example, if the feedback voltage 354 becomes smaller than thereference signal 516 (e.g., 0.1 V) in magnitude, it is determined thatthe demagnetization process has ended.

As one example, after the demagnetization process ends (e.g., at t₈),the detection signal 358 changes from the logic high level to the logiclow level (e.g., as shown by the waveform 704). As another example, theswitch 408 is open (e.g., being turned off) and the switch 416 is closed(e.g., being turned on). As yet another example, the capacitor 414 ischarged again, and the signal 420 increases in magnitude (e.g.,linearly) again as shown by the waveform 706. As yet another example,when the signal 420 reaches a threshold 714 (e.g., the reference signal422) in magnitude (e.g., at t₉), the comparator 410 changes the signal346 (e.g., CC_ctrl) from the logic low level to the logic high level(e.g., as shown by the waveform 708). In yet another example, the signal420 keeps at the threshold 714 until the end of the off-time periodT_(off2) (e.g., until t₁₀ as shown by the waveform 706). For example,the signal 368 increases in magnitude during the off-time periodT_(off2). In another example, when the signal 368 reaches the comparisonsignal 366 in magnitude at the end of the off-time period T_(off2)(e.g., at t₁₀ as shown by the waveforms 716 and 720), the signal 356changes from the logic low level to the logic high level (e.g., as shownby the waveform 718) in order to close the switch 320. As shown in FIG.6, when the rectifying diode 360 operates normally, multiple ringsappear in the feedback voltage 354 during a resonance time period (e.g.,T_(r)) from the end of the demagnetization period (e.g., t₈) to the endof the off-time period (e.g., t₁₀), as shown by the waveform 702.

FIG. 7 is a simplified timing diagram for the power conversion system300 in a constant-voltage mode under thermal runaway of the rectifyingdiode 360 according to one embodiment. The waveform 802 represents thefeedback voltage 354 as a function of time. As shown in FIG. 7, fewrings or no rings appear in the feedback voltage 354 during theresonance time period (e.g., T_(r)), which indicates that thetransformer including the primary winding 310 and the secondary winding312 does not enter a resonant status.

FIG. 8 is a simplified diagram showing a power conversion system withprimary-side sensing and regulation according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thepower conversion system 900 includes a primary winding 910, a secondarywinding 912, an auxiliary winding 914, a power switch 920, a currentsensing resistor 930, an equivalent resistor 940 for an output cable,resistors 950 and 952, a rectifying diode 960, and a controller 970. Thecontroller 970 includes a sampling component 902, a demagnetizationdetector 904, a capacitor 906, a switch 907, a reference-signalgenerator 908, a ramp-generator-and-oscillator 916, an AND gate 918, adriving component 922, an OR gate 924, comparators 926 and 928, aflip-flop component 936, a leading edge blanking (LEB) component 986,resistors 984 and 988, an error amplifier 990, a modulation component992, a protection component 903, and a constant-current (CC) component994. For example, the power switch 920 is a bipolar transistor. Inanother example, the power switch 920 is a MOS transistor. In yetanother example, the controller 970 includes terminals 972, 974, 976,978 and 980. In yet another example, the rectifying diode 960 is aSchottky diode.

According to one embodiment, the auxiliary winding 914 is magneticallycoupled to the secondary winding 912, which, with one or more othercomponents, generates an output voltage 993. For example, informationrelated to the output voltage is processed by a voltage divider of theresistors 950 and 952, and is used to generate a feedback voltage 954,which is received by the terminal 972 (e.g., terminal FB) of thecontroller 970. In another example, the sampling component 902 samplesthe feedback voltage 954 and the sampled signal is held at the capacitor906. As an example, the error amplifier 990 compares thesampled-and-held voltage 962 with a reference signal 964 generated bythe reference-signal generator 908, and outputs a comparison signal 966associated with the error of the sampled-and-held voltage 962 withrespect to the reference signal 964. As another example, the comparisonsignal 966 is received by the modulation component 992 which receives aramping signal 968 and/or a clock signal 969 from theramp-generator-and-oscillator 916 and outputs a signal 956 (e.g.,CV_ctrl).

According to another embodiment, the comparison signal 966 is used tocontrol the pulse width for PWM and/or the switching frequency for PFMin order to regulate the output voltage in a constant-voltage mode. Forexample, the demagnetization detector 904 determines the duration of ademagnetization period based on the feedback voltage 954 and outputs adetection signal 958 to the constant-current component 994 whichgenerates a signal 946 (e.g., CC_ctrl). In another example, theprotection component 903 receives the feedback voltage 954 and thedetection signal 958 and outputs a blanking signal 905 and a faultsignal 907. In yet another example, the AND gate 918 receives the signal956 (e.g., CV_ctrl), the signal 946 (e.g., CC_ctrl) and the blankingsignal 905 and outputs a signal 919 that is received by the flip-flopcomponent 936 (e.g., at a set terminal “S”). In yet another example, theflip-flop component 936 outputs a signal 937 (e.g., at a terminal “Q”)to the driving component 922. In yet another example, the drivingcomponent 922 also receives the signal 907 (e.g., fault) and outputs adrive signal 948 through the terminal 976 to affect the status of theswitch 920. In yet another example, a primary current 996 flowingthrough the primary winding 910 is sensed using the resistor 930, and acurrent-sensing signal 942 is generated through the LEB component 986and received by the comparators 926 and 928. In yet another example, thecomparator 926 receives a threshold voltage 932 (e.g., V_(thocp)), andthe comparator 928 receives another threshold voltage 901 associatedwith the comparison signal 966 (e.g., V_(comp)). In yet another example,the comparator 926 and the comparator 928 output comparison signals 934and 938 respectively, to the OR gate 924. In yet another example, the ORgate 924 outputs a signal 925 to the flip-flop component 936 (e.g., at areset terminal “R”). As an example, when the sampled-and-held voltage962 is smaller than the reference signal 964 in magnitude, the erroramplifier 990 outputs the comparison signal 966 at a logic high level.The power conversion system 900 operates in a constant-current mode, insome embodiments. For example, when the sampled-and-held voltage 962 isequal to the reference signal 964 in magnitude, the comparison signal966 has a fixed magnitude. The power conversion system 900 operates inthe constant-voltage mode, in certain embodiments.

FIG. 9 is a simplified diagram showing the protection component 903 aspart of the power conversion system 900 according to an embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.The protection component 903 includes a comparator 1002, a timercomponent 1004, an OR gate 1006, NOT gates 1008, 1016 and 1024, acounter-and-logic component 1010, flip-flop components 1012 and 1026,and a trigger component 1014. The counter-and-logic component 1010includes flip-flop components 1018, 1020 and 1022.

According to one embodiment, the comparator 1002 receives the feedbackvoltage 954 and a reference signal 1028 and output a comparison signal1030 to the OR gate 1006. For example, the OR gate 1006 also receives asignal 1032 from the NOT gate 1024 and outputs a signal 1034 to thecounter-and-logic component 1010 which outputs a signal 1036 to the NOTgate 1024. In another example, the timer component 1004 outputs a signal1038 to the flip-flop component 1012 (e.g., at a terminal “D”) whichalso receives the signal 958 (e.g., at a terminal “CLK”). In yet anotherexample, the flip-flop component 1012 outputs a signal 1042 (e.g., at aterminal “Q”) to the timer component 1004 and the trigger component 1014which provides a signal 1040 to the flip-flop component 1012 (e.g., at aterminal “R”) and the NOT gate 1016. In yet another example, theflip-flop component 1026 receives the signal 1032 (e.g., at a terminal“D”) and the blanking signal 905 (e.g., at a terminal “CLK”) and outputsthe fault signal 907 (e.g., at a terminal “Q”). In yet another example,a rising edge of the signal 1042 (e.g., q1) corresponds to a fallingedge of the signal 1038. In yet another example, the flip-flop component1018 receives the signal 1034 (e.g., at a “CLK” terminal).

FIG. 10 is a simplified timing diagram for the power conversion system900 according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The waveform 1102represents the signal 1038 as a function of time, the waveform 1104represents the feedback voltage 954 as a function of time, and thewaveform 1106 represents the signal 958 as a function of time. Inaddition, the waveform 1108 represents the signal 1042 (e.g., q1) as afunction of time, the waveform 1110 represents the blanking signal 905as a function of time, and the waveform 1112 represents the signal 1030(e.g., qr_det) as a function of time. The waveform 1114 represents thesignal 1032 (e.g., Qcounter) as a function of time, the waveform 1116represents the signal 948 (e.g., DRV) as a function of time, and thewaveform 1118 represents the fault signal 907 (e.g., fault) as afunction of time. For example, t₁₅≦t₁₆≦t₁₇≦t₁₈≦t₁₉≦t₂₀≦t₂₁≦t₂₂≦t₂₃≦t₂₄.

Referring to FIG. 8, FIG. 9 and FIG. 10, the timer component 1004changes the signal 1038 from a logic low level to a logic high levelfrom time to time (e.g., with a time interval T_(d)) as shown by thewaveform 1102, in some embodiments. For example, at t₁₅, the detectionsignal 958 changes from a logic high level to a logic low level (e.g.,as shown by the waveform 1106), which indicates the end of thedemagnetization period T_(demag3). For example, the timer component 1004outputs the signal 1038 at a logic low level (e.g., as shown by thewaveform 1102), and in response, the flip-flop component 1012 (e.g.,DFF1) outputs the signal 1042 (e.g., q1) at the logic low level (e.g.,as shown by the waveform 1108). The power conversion system 900 operatesnormally, in certain embodiments. For example, the time interval T_(d)is about 10 ms.

According to one embodiment, between t₁₅ and t₁₆, the signal 1038 keepsat the logic low level, and the signal 1042 (e.g., q1) keeps at thelogic low level. For example, the fault signal 907 keeps at the logiclow level, even if the signal 1032 (e.g., Qcounter) changes from thelogic high level to the logic low level. In another example, at t₁₆, thetimer component 1004 changes the signal 1038 from the logic low level tothe logic high level (e.g., as shown by the waveform 1102). In yetanother example, between t₁₆ and t₂₁ (e.g., T_(d)), the timer component1004 keeps the signal 1038 at the logic high level if no falling edge isdetected in the detection signal 958. In yet another example, at t₁₇,the detection signal 958 changes from the logic low level to the logichigh level (e.g., as shown by the waveform 1106), which indicates thebeginning of the demagnetization period T_(demag4). In yet anotherexample, at t₁₈, the detection signal 958 changes from the logic highlevel to the logic low level (e.g., as shown by the waveform 1106),which indicates the end of the demagnetization period T_(demag4). In yetanother example, upon detection of the falling edge in the detectionsignal 958 (e.g., at t₁₈), the timer component 1004 changes the signal1038 from the logic high level to the logic low level (e.g., as shown bythe waveform 1102). In response to the change of the signal 1038, thetrigger component 1014 changes the signal 1040, and the blanking signal905 changes from the logic high level to the logic low level, in someembodiments. For example, the flip-flop component 1012 changes thesignal 1042 (e.g., q1) from the logic low level to the logic high level(e.g., at t₁₈ as shown by the waveform 1108). The power conversionsystem 900 enters into a thermal-runaway-detection mode, in someembodiments. For example, a clock associated with the timer component1004 is restarted toward a next time interval T_(d). As an example,T_(d) is predetermined, and is longer than multiple switching periodsassociated with the power conversion system 900.

According to another embodiment, when the blanking signal 905 is at thelogic low level, i.e., during a detection period (e.g., T_(blank)), thesignal 919 from the AND gate 918 is at the logic low level so that theswitch 920 is kept open (e.g., being turned off), regardless of thesignal 956 (e.g., CV_ctrl) and the signal 946 (e.g., CC_ctrl). As anexample, a starting time of the detection period (e.g., T_(blank)) is att₁₈ and an ending time of the detection period (e.g., T_(blank)) is att₂₀. In another example, the blanking signal 905 changes from the logiclow level to the logic high level after the detection period (e.g., att₂₀, as shown by the waveform 1110). As an example, the comparatorcompares the feedback voltage 954 and the reference signal 1028 (e.g.,0.1 V), and determines whether multiple resonance rings occur in thefeedback voltage 954. As another example, the counter-and-logiccomponent 1010 determines the number of the resonance rings in thefeedback voltage 954. As yet another example, the detection period(e.g., T_(blank)) is about 20 μs. For example, a resonance ringcorresponds to the feedback voltage 954 becoming smaller than thereference signal 1028 in magnitude. In yet another example, thedetection period (e.g., T_(blank)) starts when the timer component 1004changes the signal 1038 from the logic high level to the logic lowlevel. In yet another example, the detection period (e.g., T_(blank))ends when the flip-flop component 1012 changes the signal 1042 (e.g.,q1) from the logic high level to the logic low level.

According to yet another embodiment, if the counter-and-logic component1010 determines the number of the resonance rings appearing in thefeedback voltage 954 (e.g., the feedback voltage 954 becoming smallerthan the reference signal 1028) during the detection period (e.g.,T_(blank)) reaches a threshold (e.g., 4), the signal 1032 (e.g.,Qcounter) changes to the logic low level (e.g., at t₁₉, as shown by thewaveforms 1104 and 1114), and the counter-and-logic component 1010 stopscounting. For example, upon the rising edge of the blanking signal 905(e.g., at t₂₀ as shown by the waveform 1110), the flip-flop component1026 (e.g., DFF2) detects the signal 1032 (e.g., Qcounter), and outputsthe fault signal 907 at the logic low level in response to the signal1032 being at the logic low level (e.g., as shown by the waveforms 1114and 1118). The power conversion system 900 is not in a thermal-runawaystatus, and continues to operate normally, in certain embodiments. Forexample, the driving component 922 outputs the drive signal 948 to closeor open the switch 920 according to one or more modulation frequencies.In certain embodiments, the time period between t₂₀ and t₂₁ includes oneor more switching periods. For example, the power conversion system 900enters into the thermal-runaway-detection mode during each switchingperiod. That is, during a detection period (e.g., T_(blank)) within eachswitching period, whether the number of the resonance rings appearing inthe feedback voltage 954 reaches the threshold is determined fordetecting thermal runaway.

In one embodiment, at t₂₁, another time interval T_(d) begins, and theclock associated with the timer component 1004 is restarted to count thetime. For example, the timer component 1004 changes the signal 1038 fromthe logic low level to the logic high level (e.g., at t₂₁ as shown bythe waveform 1102). In another example, at t₂₂, the detection signal 958changes from the logic low level to the logic high level (e.g., as shownby the waveform 1106), which indicates the beginning of thedemagnetization period T_(demag5). In yet another example, at t₂₃, thedetection signal 958 changes from the logic high level to the logic lowlevel (e.g., as shown by the waveform 1106), which indicates the end ofthe demagnetization period T_(demag5). In yet another example, the timercomponent 1004 changes the signal 1038 from the logic high level to thelogic low level (e.g., as shown by the waveform 1102), and in response,the flip-flop component 1012 changes the signal 1042 (e.g., 1) from thelogic low level to the logic high level (e.g., as shown by the waveform1108). The power conversion system 900 enters into thethermal-runaway-detection mode again, in some embodiments.

In another embodiment, at t₂₃, the trigger component 1014 changes thesignal 1040, and as a result the blanking signal 905 changes from thelogic high level to the logic low level. For example, the blankingsignal 905 changes from the logic low level to the logic high levelafter another detection period (e.g., T_(blank)), as shown by thewaveform 1110. In another example, during the detection period (e.g.,T_(blank)), the switch 920 is kept open (e.g., being turned off),regardless of the signal 956 (e.g., CV_ctrl) and the signal 946 (e.g.,CC_ctrl). As an example, the comparator compares the feedback voltage954 and the reference signal 1028 (e.g., 0.1 V), and determines whethermultiple resonance rings occur in the feedback voltage 954. As anotherexample, the counter-and-logic component 1010 determines the number ofthe resonance rings in the feedback voltage 954.

In yet another embodiment, if the counter-and-logic component 1010determines the number of the resonance rings in the feedback voltage 954during the detection period (e.g., T_(blank)) is smaller than thethreshold (e.g., 4), the signal 1032 (e.g., Qcounter) keeps at the logichigh level (e.g., as shown by the waveforms 1104 and 1114). For example,upon the rising edge of the blanking signal 905 (e.g., at t₂₄ as shownby the waveform 1110), the flip-flop component 1026 (e.g., DFF2) detectsthe signal 1032 (e.g., Qcounter), and changes the fault signal 907 fromthe logic low level to the logic high level in response to the signal1032 being at the logic high level (e.g., as shown by the waveforms 1114and 1118). The power conversion system 900 is determined to be in thethermal-runaway status, and enters into an auto-recovery mode or ananalog latch mode, in certain embodiments. For example, the powerconversion system 900 stops operation and there is no output signal fromthe power conversion system 900 unless the power conversion system 900is powered down (e.g., a power cord is unplugged) and restarted (e.g.,the power cord is plugged in), so that the temperature of the diode 960can decrease for the system 900 to operate safely. In another example,the demagnetization period T_(demag5) is separated from thedemagnetization period T_(demag4) by one or more switching periodsassociated with the drive signal 948.

As discussed above and further emphasized here, FIG. 10 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, a resonance ring corresponds to thefeedback voltage 954 exceeding the reference signal 1028 in magnitude.

According to one embodiment, a system controller for protecting a powerconversion system includes a protection component and a drivingcomponent. The protection component is configured to receive a feedbacksignal, a reference signal, and a demagnetization signal generated basedon at least information associated with the feedback signal, processinformation associated with the feedback signal, the reference signal,and the demagnetization signal, and generate a protection signal basedon at least information associated with the feedback signal, thereference signal, and the demagnetization signal. The demagnetizationsignal is related to multiple demagnetization periods of the powerconversion system, the multiple demagnetization periods including afirst demagnetization period and a second demagnetization period. Thedriving component is configured to receive the protection signal andoutput a drive signal to a switch configured to affect a current flowingthrough a primary winding of the power conversion system. The protectioncomponent is further configured to: process information associated withthe feedback signal and the reference signal during a first detectionperiod, the first detection period including a first starting time and afirst ending time, the first starting time being at or after a firstdemagnetization end of the first demagnetization period, determine,during the first detection period, a first number of times that thefeedback signal changes from being smaller than the reference signal tobeing larger than the reference signal in magnitude, and determinewhether the first number of times exceeds a predetermined threshold atthe first ending time. The protection component and the drivingcomponent are further configured to, in response to the first number oftimes not exceeding the predetermined threshold at the first endingtime, output the drive signal to cause the switch to open and remainopen in order to protect the power conversion system. For example, thesystem controller is implemented according to FIG. 8, and/or FIG. 9.

According to another embodiment, a system controller for protecting apower conversion system includes a protection component and a drivingcomponent. The protection component is configured to receive a feedbacksignal, a reference signal, and a demagnetization signal generated basedon at least information associated with the feedback signal, processinformation associated with the feedback signal, the reference signal,and the demagnetization signal, and generate a protection signal basedon at least information associated with the feedback signal, thereference signal, and the demagnetization signal. The demagnetizationsignal is related to multiple demagnetization periods of the powerconversion system, the multiple demagnetization periods including afirst demagnetization period and a second demagnetization period. Thedriving component is configured to receive the protection signal andoutput a drive signal to a switch configured to affect a current flowingthrough a primary winding of the power conversion system. The protectioncomponent is further configured to: process information associated withthe feedback signal and the reference signal during a first detectionperiod, the first detection period including a first starting time and afirst ending time, the first starting time being at or after a firstdemagnetization end of the first demagnetization period, determine,during the first detection period, a first number of times that thefeedback signal changes from being larger than the reference signal tobeing smaller than the reference signal in magnitude, and determinewhether the first number of times exceeds a predetermined threshold atthe first ending time. The protection component and the drivingcomponent are further configured to, in response to the first number oftimes not exceeding the predetermined threshold at the first endingtime, output the drive signal to cause the switch to open and remainopen in order to protect the power conversion system. For example, thesystem controller is implemented according to FIG. 8, and/or FIG. 9.

According to yet another embodiment, a method for protecting a powerconversion system includes: receiving a feedback signal, a referencesignal, and a demagnetization signal generated based on at leastinformation associated with the feedback signal, processing informationassociated with the feedback signal, the reference signal, and thedemagnetization signal, and generating a protection signal based on atleast information associated with the feedback signal, the referencesignal, and the demagnetization signal, the demagnetization signal beingrelated to multiple demagnetization periods of the power conversionsystem, the multiple demagnetization periods including a firstdemagnetization period and a second demagnetization period. The methodadditionally includes: receiving the protection signal, processinginformation associated with the protection signal, and outputting adrive signal to a switch configured to affect a current flowing througha primary winding of the power conversion system. The processinginformation associated with the feedback signal, the reference signal,and the demagnetization signal includes: processing informationassociated with the feedback signal and the reference signal during afirst detection period, the first detection period including a firststarting time and a first ending time, the first starting time being ator after a first demagnetization end of the first demagnetizationperiod, determining, during the first detection period, a first numberof times that the feedback signal changes from being smaller than thereference signal to being larger than the reference signal in magnitude,and determining whether the first number of times exceeds apredetermined threshold at the first ending time. The outputting a drivesignal to a switch configured to affect a current flowing through aprimary winding of the power conversion system includes: in response tothe first number of times not exceeding the predetermined threshold atthe first ending time, outputting the drive signal to cause the switchto open and remain open in order to protect the power conversion system.For example, the method is implemented according to FIG. 8, FIG. 9,and/or FIG. 10.

According to yet another embodiment, a method for protecting a powerconversion system includes: receiving a feedback signal, a referencesignal, and a demagnetization signal generated based on at leastinformation associated with the feedback signal, processing informationassociated with the feedback signal, the reference signal, and thedemagnetization signal, and generating a protection signal based on atleast information associated with the feedback signal, the referencesignal, and the demagnetization signal, the demagnetization signal beingrelated to multiple demagnetization periods of the power conversionsystem, the multiple demagnetization periods including a firstdemagnetization period and a second demagnetization period. The methodfurther includes: receiving the protection signal, processinginformation associated with the protection signal, and outputting adrive signal to a switch configured to affect a current flowing througha primary winding of the power conversion system. The processinginformation associated with the feedback signal, the reference signal,and the demagnetization signal includes: processing informationassociated with the feedback signal and the reference signal during afirst detection period, the first detection period including a firststarting time and a first ending time, the first starting time being ator after a first demagnetization end of the first demagnetizationperiod, determining, during the first detection period, a first numberof times that the feedback signal changes from being larger than thereference signal to being larger than the reference signal in magnitude,and determining whether the first number of times exceeds apredetermined threshold at the first ending time. The outputting a drivesignal to a switch configured to affect a current flowing through aprimary winding of the power conversion system includes: in response tothe first number of times not exceeding the predetermined threshold atthe first ending time, outputting the drive signal to cause the switchto open and remain open in order to protect the power conversion system.For example, the method is implemented according to FIG. 8, FIG. 9,and/or FIG. 10.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system controller for protecting a powerconversion system, the system controller comprising: a protectioncomponent configured to receive a feedback signal, a reference signal,and a demagnetization signal generated based at least in part on thefeedback signal and to generate a protection signal based at least inpart on the feedback signal, the reference signal, and thedemagnetization signal, the demagnetization signal being related tomultiple demagnetization periods of the power conversion system, themultiple demagnetization periods including a first demagnetizationperiod and a second demagnetization period; wherein the protectioncomponent is further configured to: process the feedback signal and thereference signal during a first detection period, the first detectionperiod including a first starting time and a first ending time, thefirst starting time being at or after a first demagnetization end of thefirst demagnetization period; determine, during the first detectionperiod, a first number of times that the feedback signal changes frombeing smaller than the reference signal to being larger than thereference signal in magnitude; and determine whether the first number oftimes exceeds a predetermined threshold at the first ending time;wherein the system controller is configured to, in response to the firstnumber of times not exceeding the predetermined threshold at the firstending time, output a drive signal to cause a switch to open and remainopen in order to protect the power conversion system, the switch beingconfigured to affect a current flowing through a primary winding of thepower conversion system.
 2. The system controller of claim 1 wherein thesystem controller is further configured to, in response to the firstnumber of times not exceeding the predetermined threshold at the firstending time, output the drive signal to cause the switch to open andremain open until the power conversion system is powered down andrestarted.
 3. The system controller of claim 1 wherein the systemcontroller is further configured to, in response to the first number oftimes exceeding the predetermined threshold at the first ending time,output the drive signal to close and open the switch according to one ormore modulation frequencies to operate the power conversion system. 4.The system controller of claim 1 wherein the protection componentincludes: a comparator configured to receive the feedback signal and thereference signal and generate a comparison signal based at least in parton the feedback signal and the reference signal; and a processingcomponent configured to receive the comparison signal and output a firstprocessed signal based at least in part on the comparison signal, thefirst processed signal being related to the first number of times thatthe feedback signal changes from being smaller than the reference signalto being larger than the reference signal in magnitude.
 5. The systemcontroller of claim 4 wherein the processing component is furtherconfigured to, in response to the first number of times not exceedingthe predetermined threshold, keep the first processed signal at a firstlogic level.
 6. The system controller of claim 5 wherein the processingcomponent is further configured to, in response to the first number oftimes exceeding the predetermined threshold, change the first processedsignal from the first logic level to a second logic level.
 7. The systemcontroller of claim 4 wherein the processing component includes: an ORgate configured to receive the comparison signal and generate an inputsignal based at least in part on the comparison signal; and a counterconfigured to receive the input signal and generate an output signalbased at least in part on the input signal, the output signal beingrelated to the first processed signal.
 8. The system controller of claim7 wherein the processing component further includes: a first NOT gateconfigured to receive the demagnetization signal and output a secondprocessed signal to the counter based at least in part on thedemagnetization signal; and a second NOT gate configured to receive theoutput signal and output the first processed signal based at least inpart on the output signal.
 9. The system controller of claim 8 whereinthe counter includes one or more flip-flop components configured toreceive the input signal and the second processed signal and generatethe output signal based on at least information associated with theinput signal and at least in part on the second processed signal. 10.The system controller of claim 7 wherein the OR gate is furtherconfigured to receive the first processed signal and generate the inputsignal based at least in part on the comparison signal and the firstprocessed signal.
 11. The system controller of claim 4, furthercomprising: a timer configured to generate a timing signal associatedwith one or more pulses; a first flip-flop component configured toreceive the timing signal and the demagnetization signal and generate atrigger signal based at least in part on the timing signal and thedemagnetization signal; and a trigger configured to receive the triggersignal and generate an output signal based at least in part on thetrigger signal.
 12. The system controller of claim 11 wherein the timeris further configured to receive the trigger signal.
 13. The systemcontroller of claim 11 wherein the protection component is furtherconfigured to, if the timing signal is at a logic high level before thefirst demagnetization end and the timing signal changes from the logichigh level to a logic low level in response to the first demagnetizationend, determine, during the first detection period, the first number oftimes that the feedback signal changes from being smaller than thereference signal to being larger than the reference signal in magnitude.14. The system controller of claim 11 wherein the processing componentfurther includes: a second flip-flop component configured to: receivethe first processed signal; and in response to the first number of timesnot exceeding the predetermined threshold at the first ending time,output the protection signal at a logic level based at least in part onthe first processed signal in order to cause the switch to open andremain open in order to protect the power conversion system.
 15. Thesystem controller of claim 11 wherein the first ending time is at orbefore an end of an off-time period including the first demagnetizationperiod.
 16. The system controller of claim 15 wherein the switch remainsopen during the off-time period.
 17. The system controller of claim 11wherein the protection component is further configured to, during asecond detection period, process the feedback signal and the referencesignal and determine a second number of times that the feedback signalchanges from being smaller than the reference signal to being largerthan the reference signal in magnitude, the second detection periodbeing separated from the first detection period by one or more switchingperiods associated with the drive signal.
 18. The system controller ofclaim 17 wherein the second detection period includes a second startingtime and a second ending time, the second starting time being at orafter a second demagnetization end of the second demagnetization period.19. The system controller of claim 11, further comprising: an AND gateconfigured to receive the protection signal and generate a thirdprocessed signal based at least in part on the protection signal; and athird flip-flop component configured to receive the third processedsignal and output a flip-flop signal to a driver based at least in parton the third processed signal.
 20. The system controller of claim 1,further comprising a demagnetization detector configured to receive thefeedback signal and generate the demagnetization signal based at leastin part on the feedback signal.
 21. The system controller of claim 1wherein the second demagnetization period is separated from the firstdemagnetization period by one or more switching periods associated withthe drive signal.
 22. A system controller for protecting a powerconversion system, the system controller comprising: a protectioncomponent configured to receive a feedback signal, a reference signal,and a demagnetization signal generated based at least in part on thefeedback signal and to generate a protection signal based at least inpart on the feedback signal, the reference signal, and thedemagnetization signal, the demagnetization signal being related tomultiple demagnetization periods of the power conversion system, themultiple demagnetization periods including a first demagnetizationperiod and a second demagnetization period; wherein the protectioncomponent is further configured to: process the feedback signal and thereference signal during a first detection period, the first detectionperiod including a first starting time and a first ending time, thefirst starting time being at or after a first demagnetization end of thefirst demagnetization period; determine, during the first detectionperiod, a first number of times that the feedback signal changes frombeing larger than the reference signal to being smaller than thereference signal in magnitude; and determine whether the first number oftimes exceeds a predetermined threshold at the first ending time;wherein the system controller is configured to, in response to the firstnumber of times not exceeding the predetermined threshold at the firstending time, output a drive signal to cause a switch to open and remainopen in order to protect the power conversion system, the switch beingconfigured to affect a current flowing through a primary winding of thepower conversion system.
 23. The system controller of claim 22 whereinthe system controller is further configured to, in response to the firstnumber of times not exceeding the predetermined threshold at the firstending time, output the drive signal to cause the switch to open andremain open until the power conversion system is powered down andrestarted.
 24. The system controller of claim 22 wherein the systemcontroller is further configured to, in response to the first number oftimes exceeding the predetermined threshold at the first ending time,output the drive signal to close and open the switch according to one ormore modulation frequencies to operate the power conversion system. 25.The system controller of claim 22 wherein the protection componentincludes: a comparator configured to receive the feedback signal and thereference signal and generate a comparison signal based at least in parton the feedback signal and the reference signal; and a processingcomponent configured to receive the comparison signal and output aprocessed signal based at least in part on the comparison signal, theprocessed signal being related to the first number of times that thefeedback signal changes from being larger than the reference signal tobeing smaller than the reference signal in magnitude.
 26. The systemcontroller of claim 25 wherein the processing component includes: an ORgate configured to receive the comparison signal and generate an inputsignal based at least in part on the comparison signal; and a counterconfigured to receive the input signal and generate an output signalbased at least in part on the input signal, the output signal beingrelated to the processed signal.
 27. The system controller of claim 26wherein the OR gate is further configured to receive the processedsignal and generate the input signal based at least in part on thecomparison signal and the processed signal.
 28. The system controller ofclaim 25 wherein the processing component is further configured to, inresponse to the first number of times not exceeding the predeterminedthreshold, keep the processed signal at a first logic level.
 29. Thesystem controller of claim 28 wherein the processing component isfurther configured to, in response to the first number of timesexceeding the predetermined threshold, change the processed signal fromthe first logic level to a second logic level.
 30. The system controllerof claim 25, further comprising: a timer configured to generate a timingsignal associated with one or more pulses; a first flip-flop componentconfigured to receive the timing signal and the demagnetization signaland generate a trigger signal based at least in part on the timingsignal and the demagnetization signal; and a trigger configured toreceive the trigger signal and generate an output signal based at leastin part on the trigger signal.
 31. The system controller of claim 30wherein the processing component further includes: a second flip-flopcomponent configured to: receive the processed signal; and in responseto the first number of times not exceeding the predetermined thresholdat the first ending time, output the protection signal at a logic levelbased at least in part on the processed signal in order to cause theswitch to open and remain open in order to protect the power conversionsystem.
 32. The system controller of claim 30 wherein the first endingtime is at or before an end of an off-time period including the firstdemagnetization period.
 33. The system controller of claim 32 whereinthe switch remains open during the off-time period.
 34. The systemcontroller of claim 25 wherein the protection component is furtherconfigured to, if the timing signal is at a logic high level before thefirst demagnetization end and the timing signal changes from the logichigh level to a logic low level in response to the first demagnetizationend, determine, during the first detection period, the first number oftimes that the feedback signal changes from being larger than thereference signal to being smaller than the reference signal inmagnitude.
 35. The system controller of claim 25 wherein the protectioncomponent is further configured to, during a second detection period,process the feedback signal and the reference signal and determine asecond number of times that the feedback signal changes from beinglarger than the reference signal to being smaller than the referencesignal in magnitude, the second detection period being separated fromthe first detection period by one or more switching periods associatedwith the drive signal.
 36. The system controller of claim 35 wherein thesecond detection period includes a second starting time and a secondending time, the second starting time being at or after a seconddemagnetization end of the second demagnetization period.
 37. The systemcontroller of claim 22 wherein the second demagnetization period isseparated from the first demagnetization period by one or more switchingperiods associated with the drive signal.
 38. A method for protecting apower conversion system, the method comprising: receiving a feedbacksignal, a reference signal, and a demagnetization signal generated basedat least in part on the feedback signal; processing the feedback signal,the reference signal, and the demagnetization signal; generating aprotection signal based at least in part on the feedback signal, thereference signal, and the demagnetization signal, the demagnetizationsignal being related to multiple demagnetization periods of the powerconversion system, the multiple demagnetization periods including afirst demagnetization period and a second demagnetization period; andoutputting a drive signal; wherein the processing the feedback signal,the reference signal, and the demagnetization signal includes:processing the feedback signal and the reference signal during adetection period, the detection period including a starting time and anending time, the starting time being at or after a demagnetization endof the first demagnetization period; determining, during the detectionperiod, a number of times that the feedback signal changes from beingsmaller than the reference signal to being larger than the referencesignal in magnitude; and determining whether the number of times exceedsa predetermined threshold at the ending time; wherein the outputting adrive signal includes: in response to the number of times not exceedingthe predetermined threshold at the ending time, outputting the drivesignal to cause a switch to open and remain open in order to protect thepower conversion system.
 39. The method of claim 38 wherein theoutputting the drive signal to cause the switch to open and remain openin order to protect the power conversion system includes outputting thedrive signal to cause the switch to open and remain open until the powerconversion system is powered down and restarted.
 40. The method of claim38, wherein the ending time is at or before an end of an off-time periodincluding the first demagnetization period.
 41. The method of claim 40,wherein the switch remains open during the off-time period.
 42. A methodfor protecting a power conversion system, the method comprising:receiving a feedback signal, a reference signal, and a demagnetizationsignal generated based at least in part on the feedback signal;processing the feedback signal, the reference signal, and thedemagnetization signal; generating a protection signal based at least inpart on the feedback signal, the reference signal, and thedemagnetization signal, the demagnetization signal being related tomultiple demagnetization periods of the power conversion system, themultiple demagnetization periods including a first demagnetizationperiod and a second demagnetization period; and outputting a drivesignal; wherein the processing the feedback signal, the referencesignal, and the demagnetization signal includes: processing the feedbacksignal and the reference signal during a detection period, the detectionperiod including a starting time and an ending time, the starting timebeing at or after a demagnetization end of the first demagnetizationperiod; determining, during the detection period, a number of times thatthe feedback signal changes from being larger than the reference signalto being smaller than the reference signal in magnitude; and determiningwhether the number of times exceeds a predetermined threshold at theending time; wherein the outputting a drive signal includes: in responseto the number of times not exceeding the predetermined threshold at theending time, outputting the drive signal to cause a switch to open andremain open in order to protect the power conversion system.
 43. Themethod of claim 42 wherein the outputting the drive signal to cause theswitch to open and remain open in order to protect the power conversionsystem includes outputting the drive signal to cause the switch to openand remain open until the power conversion system is powered down andrestarted.
 44. The method of claim 42, wherein the ending time is at orbefore an end of an off-time period including the first demagnetizationperiod.
 45. The method of claim 44, wherein the switch remains openduring the off-time period.